The present invention relates to an ultrasonic image output apparatus having a function for displaying, as an ultrasonic image, information obtained by transmitting/receiving an ultrasonic wave to/from an object to be examined or reproduction data from an image recording/reproducing device such as a video tape recorder (VTR) which records the data, and a function for displaying a desired frame of the ultrasonic image as a still image and recording it as a hard copy.
In an ultrasonic diagnosing apparatus, information obtained by transmitting/receiving an ultrasonic wave to/from an object is generally displayed as an ultrasonic image, mainly as a slice image. When the ultrasonic image is displayed, an image data signal obtained by ultrasonic scanning is converted into a video signal for television scanning by a so-called scan converter and the video signal is supplied to a display system.
In a conventional ultrasonic diagnosing apparatus, ultrasonic images derived from information obtained by transmitting/receiving an ultrasonic wave to/from an object are temporarily stored as a video signal in an image recording/reproducing device such as a VTR, and the ultrasonic images reproduced from the VTR are displayed on a cathode ray tube (CRT), thus allowing diagnosis. In an ultrasonic diagnosing apparatus of this type, a size or an area of a desired portion of a still image from a desired frame of an ultrasonic image stored in a memory as the video signal can be measured, i.e., calipered. With this apparatus, diagnosis or measurement can be performed after examination by using the ultrasonic image recorded in the VTR.
Another ultrasonic diagnosing apparatus can record an M mode image such as an ultrasonic cardiograph (UCG) using a recording device, e.g., a line scan recorder. The line scan recorder, for example, records a line scan image by moving continuous photosensitive recording paper in units of scanning lines using an optical fiber tube. In addition, in an ultrasonic diagnosing apparatus of this type, a desired frame of the ultrasonic image is temporarily stored in a memory and a hard copy can be formed by the line scan recorder. In this apparatus, in order to form the hard copy, a line image signal is supplied to the line scan recorder in accordance with a recording speed thereof. For reference in the next examination, the hard copy can be utilized for keeping records of ultrasonic still images.
In the conventional ultrasonic diagnosing apparatus which can make a hard copy of a desired frame with a line scan recorder, a video signal of the ultrasonic image from the VTR is converted into digital data by an analog/digital (A/D) converter and is then written in a frame memory. The image data written in the frame memory is read out and converted into an analog signal by a digital/analog (D/A) converter. This analog signal is supplied to a display. When a writing operation in the frame memory is terminated, a displayed image is frozen into a still image. When the image data is read out from the frame memory in order to be supplied to the display, it is partially or entirely written in a buffer memory. Information in the buffer memory is read out in accordance with the recording speed of the line scan recorder and converted into an analog signal by the D/A converter so as to be recorded by the line scan recorder.
The line scan recorder uses continuous recording paper. For this reason, when an M mode image is recorded directly on the recording paper, the longitudinal direction of the paper corresponds to a time base direction and the transverse direction thereof corresponds to the vertical direction of the M mode image. Therefore, when ultrasonic images are recorded along the same direction as the M mode image, all the images on the recording paper are aligned in the same direction, thus allowing for easy operation. In the apparatus of this type, since a scanning line direction of the video signal differs by 90 degrees from that of the line scan recorder, scan conversion must be performed by the buffer memory. For example, when a buffer memory has a capacity corresponding to one vertical line of the video frame, every time the video signals of one frame are read from the buffer memory for transfer to the display, one vertical line of pixel data of the video frame is written in the buffer memory. The pixel data is written in the buffer memory by sampling in synchronism with the transfer of the corresponding pixels to the display. The one vertical line of pixel data is supplied to the line scan recorder so that the image data for one line is recorded thereby. This sampling operation is repeated for each read operation of the frame to the display. When the sampling operation is repeated for the number of times corresponding to the number of pixels for one horizontal line, the recording operation of the image for one frame ends. In this case, a recording speed is determined by a frame repeating period of the video signal (e.g., about 33.3 ms) and the number of pixels in one horizontal line of the video frame. For this reason, even if the line scan recorder has a sufficient margin in speed, the recording speed cannot be increased. In addition, a complicated synchronous sampling process is required for fetching the data in the buffer. In this case, in order to increase the recording speed, the capacity of the buffer memory is increased so as to correspond to several vertical lines of the video frame. However, a memory having a large capacity is needed, and the sampling operation and the write/read control of the memory become cumbersome. Since the video signal is obtained by interlaced scanning, sampling is more complicated than that of noninterlaced scanning.
If the scanning direction of the video signal coincides with that of the line scan recorder, the video signal can be read without sampling a predetermined number of pixel data in a scanning line of the video frame. However, a scanning speed along a longitudinal direction of the recording paper of the line scan recorder is determined by a feeding speed of the paper, which is slower than the vertical scanning speed of the video signal. For this reason, buffering by means of a memory is needed. In addition, as described above, the video signal is obtained by interlaced scanning. Therefore, in order to record a video signal by a line scan recorder which performs substantially noninterlaced scanning, a buffer memory having a capacity of at least one field is required. Furthermore, in this case, since the vertical direction of the video image corresponds to the longitudinal direction of the recording paper, it is different from the recording direction of the M mode image, resulting in inconvenience.